Will we have a Christmas comet in 2013?

A comet discovery on Sept. 24, 2012 has the astronomical community abuzz concerning its possible appearance in our skies at some point in late 2013.

The comet in question is designated C/2012 S1 (ISON). ISON stands for the International Scientific Optical Network located near Kislovodsk, Russia. Astronomers Artyom Novichonok and Vitali Nevski imaged the comet using a 0.4 meter reflecting telescope.

At magnitude +18 in the constellation Cancer, the comet is not currently much to look at. What makes this discovery especially interesting, though, is its relatively large discovery distance coupled with its interesting orbital geometry near perihelion – the point at which it will be closest to the Sun – in Nov. 2013.

Comet C/2012 C1 ISON is currently just over 6.6 astronomical units from Earth. In comparison, Hale-Bopp was 7.2 astronomical units away during its initial discovery. Jupiter and Saturn have semi-major axes of 5.2 & 9.5 A.U.s, respectively.

Comet Lovejoy as seen from the International Space Station in late 2011. NASA

So, how bright will Comet ISON get? Well, comets are notoriously fickle beasts. One only has to look back at Comet Kohoutek in 1973 to see a great comet that wasn’t. Still, other Sungrazers, such as Comet Ikeya-Seki in 1965 and Comet Lovejoy earlier this year, made the ranks of the Great Comets.

Much speculation hinges on if Comet ISON survives its perihelion passage on November 28th 2013. On this date, Comet ISON will pass within 0.012 A.U.s or just over a 1.8 million kilometres from the Sun. Keep in mind, that the Sun itself is about 1.4 million kilometres in diameter. The entire comet could simply melt away at those relatively short distances.

But there is precedent for such a scorching passage: Kreutz sungrazer Comet Lovejoy passed only 145,000 kilometres above the photosphere and survived to become a great daylight comet in early 2012.

Comet ISON has an almost parabolic orbit suggestive of an initial visitor to the inner solar system from the Oort Cloud. This also bodes well for an active and energetic nucleus. Researcher John Bortle also notes similarities between the path of Comet ISON and the Great Comet of 1680.

Interestingly, Comet ISON also passes less than 0.1 A.U. from Mars in late September 2013, making it a possible visual target for Mars Curiosity which is currently exploring its new home in Gale Crater. To our knowledge, an image of a comet from the surface of another world hasn’t been done before.

Looking East: Comet ISON on the morning of November 24th, 2014, about an hour before sunrise from mid-northern latitudes. Created by the author in Starry Night

Comet ISON should also reach naked eye brightness (greater than +6 magnitude) as seen from Earth, as it crosses into the constellation Leo in September 2013. It will stand about 47 degrees from the Sun in the morning sky on October 1st, and passes only 1 degree from Mars and 2 degrees from Regulus on October 16th.

Note that there’s also a hybrid solar eclipse (i.e. an eclipse that’s annular along part of the track and total along another portion) across the mid-Atlantic & Central Africa on November 3rd, 2013 with the comet is less than 50° degrees away.

Comet ISON is projected to reach negative magnitudes just days before perihelion of November 28, but will be extremely close to the Sun for observation. It will also pass within five degrees of Saturn and Mercury and just a degree from +4th magnitude Comet Encke (2P) placed low in the dawn on the morning of November 24th.

The path on Comet ISON into the morning sky for the first two weeks of December 2013. Created by the Author using Starry Night

After a brief dip into the southern hemisphere, the real show may begin. Unlike Comet Lovejoy, Comet ISON will be well placed for northern hemisphere observers in mid to late December 2013.

If it survives perihelion, it may unfurl a magnificent dust tail in the dawn sky as it heads through the constellations Serpens Caput, Hercules, and Corona Borealis. A comet’s dust tail is swept back from solar wind pressure, and can actually extend in front of its path as it journeys back out of the solar system.

In fact, Comet ISON may still shine at a respectable magnitude +3 on Christmas Day 2013 and also just might become the great Christmas comet of 2013. Incidentally, comets are named after their discoverers and those discoveries are now made by automated surveys and satellites as opposed to lone dedicated amateur hunters. Hence names like “SOHO” and “LINEAR” that now grace many comets.

One of my favourites in the bizarre name category was Comet IRAS-Araki-Alcock that passed only 0.0312 A.U.s from the Earth (just under 12 times the Earth-Moon distance) in 1983.

And to head off the inevitable “Comet Elenin” hype that seems to follow any bright new comet discovery; Comet ISON isn’t a threat to the Earth. It will only pass about 0.4 A.U.s (just over 59 million kilometres) from Earth in early January 2014. This is just close enough to provide a good show. So, put away those anti-cyanide “comet pills” that your grandparents stashed away for the Great Comet of 1910 and enjoy the show.

Bruce Willis can stay home for this one!

2013 is already shaping up to be a great year for comets, with Comet Pan-STARRS (C/2011 L4) set to put on a fine performance in March of 2013 for southern hemisphere viewers. It’ll be fascinating to watch the passage of both comets as observations refine their orbits and a battery of cameras and telescopes await them, both in space & Earth-bound.

Science journalist, astronomy specialist, educator. Retired from the USAF in 2007 and am now a science teacher and freelance science writer. Am out stargazing on every clear night and hope to add science... read more fiction writer to my resume!View author's profile